Since 2002, there has been a general trend of increasing oil prices. This trend is generally expected to continue as a result of a number of factors: increasing oil demand from emerging economies; geopolitical instability in important production areas; and reduced exploration and technological development within the last two decades due to low oil prices.
Current oil prices, along with international regulations on CO2 emissions (such as the Kyoto Protocol and beyond, Alberta “carbon tax”, California regulation on GHG footprint of fossil fuels, etc.) increases the industries interest in providing innovative solutions that will allow: the increase of oil recovery from a given existing reservoir at a reduced additional cost; reliable performance within a large range of oil/reservoir characteristics; and the reduction of carbon footprint of technologies for enhanced oil recovery.
The techniques to be employed for oil recovery depend on the particular geological conditions (thin reservoirs . . . , porous reservoirs . . . ) and are typically performed at different stages of the oil production.
The term Primary Recovery Technologies includes recovery strategies using the natural energy of reservoirs. These technologies are based on the immiscible fluids displacement, and different mechanisms are possible, such as: Gas Cap drive (expansion of the gas phase); Solution Gas Drive (ex-solution of solved Gas); Bottom Water Drive (aquifer displacement). For conventional oil typical performance for primary recovery techniques are around 19% of OOIP (Original Oil in Place): less for heavy oils, more for light oils.
In the Secondary Recovery, also known as water-flooding, the enhancement of oil production is performed by adding energy to the natural system. Water is typically injected in a well (or a pattern of wells) in order to maintain pressure in the reservoir and to displace oil towards a producer. Initially oil alone is produced. Then as water component progresses, both oil and water are produced. As time advances, the percentage of water (the watercut) increases progressively. For conventional oil, average recovery by Water Flooding is around 32% OIP (Oil In Place) after primary recovery.
Enhanced Oil Recovery (EOR) techniques are used to further increase the amount of recovered oil, in particular when water-flooding is not effective (or efficient). Some of the various EOR techniques that may be employed include: thermal-based oil recovery: steam flooding , cyclic thermal injection, in-situ combustion; electric heating, microwaves heating; chemical flooding: polymer flooding, micellar flooding; Immiscible Flooding: Nitrogen injection, CO2 injection; Miscible Flooding: lean gas injection, CO2 injection; and microbial injection.
For conventional oil, primary recovery is usually followed by water-flooding, but most of the enhanced oil technologies are not yet commercially proven. For unconventional oil reserves such as extra heavy oil in Venezuela and Albertan oil sands (characterized by high densities and high viscosities (20>API>7, 10000cPo<m<100cPo or 12>API<7, m>10000cPo) primary and secondary recovery are not sufficient to guarantee oil production and the economic exploitation of these resources is strictly related to the successful development of EOR technologies. The growing relevance of heavy oils in the world oil reserves and in particular of such unconventional oils results in the development of new EOR methods.
The SAGD (Steam Assisted Gravity Drainage) is a steam flooding technique improved by the use of two horizontal wells: one for steam injection and one for bitumen extraction. The steam heats the formation increasing the viscosity of bitumen which can flow trough the producer. The main drawback of SAGD concerns high SOR (steam on oil ratio), ranging from 2 to 4. The performance of SAGD are strictly dependent upon reservoir properties. Characteristics such gas caps, aquifers, and shale in the reservoir can result in uneconomical operations.
Steam flooding and SAGD are typically only efficient for shallow reservoirs (<1000 m) thus not being a viable solution for heavy oil resources in area such as the Arabic gulf and Russia.
The VAPEX (Vapor Extraction) process involves injecting a gaseous hydrocarbon solvent into the reservoir where it dissolves into the bitumen. The bitumen then becomes less viscous and can drain into a lower horizontal well and be extracted. The solvent is typically propane, butane, or CO2 along with a carrier gas. Main drawbacks of this technique are the following. In the case of bitumen or extra heavy oil, blending oil with the solvent without heating the formation produces only small improvements in oil recovery. Solvent is also expensive, can be scarce, and therefore the losses in the reservoir can be important.
A number of process such as ES-SAGD, LASER or SAVEX are under development in order to provide an hybrid in-situ extraction technology coupling the advantages of steam injection (thermal reduction of oil viscosity) and solvent injection. Lights hydrocarbons are used and solutions to drawbacks such as reservoir depressurization and solvent losses have to be developed. None of these combine the advantages of thermal extraction and miscible and immiscible flooding.
The In-Situ Combustion(ISC) process is defined as “the propagation of a high temperature front for which the fuel is a coke-like substance, laid down by thermal cracking reactions”. In recent years, that has been a worldwide interest of ISC for conventional oil.
Compared to mining, SAGD and VAPEX, in-situ combustion based bitumen extraction has the potential to be applied in a wider range of reservoir characteristics and to provide partially upgraded bitumen with better thermal efficiency and reduced environmental impact: Benefits of ISC include: reduced GHG footprint—50% less than SAGD; almost no water consumption; no need for land remediation. Within the ISC, bitumen is partially upgraded in the underground, and the production is performed by thermal flooding (viscosity reduction) and gas flooding (flue gas drive).
The use of oxygen injection represents one of the main areas of development for this technology. Advantages of oxygen injection for In-Situ combustion operations include: lower compression cost; simple ignition; better thermal efficiency: produced heat is not dispersed trough an inert gas; and easier downstream operations: emulsions are easy to break. Additionally, as in the case of surface oxy-combustion, the use of oxygen will result in the possibility of recovering a CO2-rich stream at the production well, to be used for additional EOR and storage. However, low oil prices and lack of GHG emissions regulations have not justified the use of oxygen in the last twenty years.
There is a need in society for an in-situ combustion oil recovery process that will improve the economics, improve the oil recovery, reduce the environmental impact, and improve safety.